1. Field of the Invention
This invention relates to printer mechanisms and more particularly to a paper transport system for printer mechanisms.
2. Prior Art
Printers, such as the type used in connection with electronic data processing systems or so-called hard copy printers, and particularly matrix printers, are normally utilized in connection with continuous form paper and therefore are provided with motor driven transport devices for moving the continuous form paper past a printing station area. Such transport devices frequently consist of two pin belt tractors which are displaceable along a guide strip and received around drive shafts. The guide strip extends transversely of the direction of movement of the paper past the printing station area as do the drive shafts. By making the tractor assemblies movable, it is possible to accommodate varying widths of paper. Such transport devices are disclosed, for example, in German OS No. 28 27 125.
Since such printers are often desired to be used in connection with single sheets of paper, or in connection with multi-sheet form paper, such as carbon copy sets, it has been known to design the tractor transport mechanism so as to be removable from the remainder of the printer. In such cases, the transport device, including the paper tractors and the allocated motor drive, are removable from the main portion of the printer and are then replaced by means specifically designed for single sheets, such as platen assemblies.
When such prior art printers are used in connection with multiple form sets, a problem arises in that the individual copies of the multiple form set may shift relative to one another, so that non-aligned printing will be reproduced on underlying form sheets. Moreover, in systems that require an exchange of different mechanisms, one for tractor transport of continuous paper forms, such as side margin perforated papers, and one for single sheet or multi-carboned forms, change over is cumbersome and it is necessary for storage space to be provided adjacent the printer for storage of the non-presently used mechanism. Of course, additionally, removal and exchange provide opportunities for mechanism damage.
It would therefore be an advance in the art to design a paper transport assembly for printers such that the assembly is readily utilizable with minor modifications for both transporting individual sheets and continuous paper and which is utilizable in a standard format fashion which minimizes the misalignment of multiple form sets.